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CARBOLIC ACID

331

convenient to dilute the sample with an equal volume of ligroin, the volume
of the latter being then subtracted from that of the neutral oils separating.

As a control, the alkaline layer maybe separated, acidified in a graduated
cylinder and the volume of the phenols separating read.

More exact results are obtained as follows: 120 grams of the carbolic
acid to be examined are distilled until only about 8 grams of residue remain
in the flask, the distillate being dissolved in ether and shaken repeatedly
in a separating funnel with 10% caustic soda solution. The total alkaline
liquid is washed several times with ether and then acidified with hydro-
chloric acid diluted with an equal volume of water, the acid liquid thus
obtained being extracted repeatedly with ether in a separating funnel to
dissolve the phenols. The ethereal solution of the latter is washed with
water and placed in a weighed flask, almost all the ether being distilled off;
the flask is then closed by a stopper through which passes a vertical bulb
tube and a thermometer, and the last portions of ether then evaporated,
care being taken that the temperature does not exceed 100°; the cold flask
is then re-weighed, the increase in weight representing the phenols.

When the phenol is not accompanied by its homologues (cresols, etc.),
it may be determined volumetrically by Seubert and Beckurts' modification
of Koppeschaar's method:

Use is made of a solution of potassium bromide and bromate in the
proportions, sKBr + KBrOs, which in presence of an acid liberates bromine
according to the equation : sKBr + KBr03 + 6HC1 = 6KC1 + 3Br2 +
3H20. About i gram of the sample (or more, if poor in phenol) is weighed
and dissolved in water to a litre, 25 c.c. of this solution being vigorously
shaken, in a bottle with a ground stopper, with 50 c.c. of potassium bromide
solution (6 grams1 per litre), 50 c.c. of potassium bromate solution (1-671
gram per litre), and 5 c.c. of cone, sulphuric acid. After a rest of 15 minutes,
10 c.c. of potassium iodide solution (i25^grams per litre) are added and the
iodine liberated titrated with decinormal thiosulphate in presence of starch
paste. The amount of phenol contained in the 25 c.c. of solution used is
found by multiplying the number of c.c. of decinormal thiosulphate used
by 0-001567 and subtracting the product from 0-047.

3.  Determination of the Water.—(a) In crude products, this is effected
by distilling 100 c.c. through a condenser and collecting the water in a
graduated cylinder until about 10 c.c. of phenols are collected under the
water.   The volume of the upper layer, plus 5 c.c., gives the percentage of
water in the product distilled.    If any neutral oils are floating on the water,
their volume is subtracted.

(6) With less impure products, 50 c.c. of the substance are shaken, in
a 100 c.c. graduated cylinder reading to 0-2 c.c., with 25 c.c. of saturated
salt solution and the aqueous layer allowed to separate: its increase in
volume indicates the amount of water in the sample.

4.  Determination of the Solidification Point.—This is made in the
Shukoff apparatus (see Mineral Oils, Paraffin, 2), 50 grams of the fused
phenol being introduced into .the inner tube and allowed to cool slowly

1 Owing to the slight admixture of potassium chloride, 6 grams are taken instead
of 5-95- p. 520.